Research On Isolation,Identification And Nitrogen Removal Characteristics Of Salt-Tolerant Nitrogen Removal Bacteria

With the rapid development of industry and agriculture,nitrogen pollution has become the main cause of water pollution,and the discharged wastewater is complicated and difficult to treat,which brings many challenges to the traditional biological nitrogen removal process.Heterotrophic nitrification-Aerobic denitrification is a popular biological nitrogen removal technology in recent years.Compared with physical chemical and traditional biological nitrogen removal methods,it has the advantages of simple process,space saving,low operating cost,high nitrogen removal efficiency,nitrogen pollution removal and COD reduction.In this study,an efficient heterotrophic nitrification-aerobic denitrification strain JG441 with strong tolerance to complex environment was screened from the wastewater discharged from preserved food factory by nitrification and denitrification medium.It was preliminarily identified as Bacillus Velezensis by bacterial colony morphology,Gram staining and 16S r DNA.According to the single factor experiment of carbon source,C/N,p H,temperature and shaking speed,the nitrogen removal efficiency was the highest when the carbon source was glucose,C/N 14,p H7,temperature 20-35℃and shaking speed 120 r/min.In the heterotrophic nitrification experiment with ammonium sulfate as the only nitrogen source,the removal rate of NH₄⁺-N is 99.7%after 24 h culture,and the highest nitrogen removal rate is 15.58 mg/L/h at 3～6 h.The COD removal rate is 77.3%,and there is almost no accumulation of NO₂^--N in the whole process.In the aerobic denitrification experiment with potassium nitrate as the only nitrogen source,the NO₃^--N removal rate was 95.9%at 24 h,the maximum NO₂^--N accumulation was 1.35 mg/L at 21 h,and the maximum NO₃^--N removal rate was 10.65 mg/L/h.When ammonium sulfate and potassium nitrate were used as mixed nitrogen sources,the strain could perform heterotrophic nitrification and aerobic denitrification at the same time,but the strain preferentially used NH₄⁺-N for nitrification and produced nitrification product NO₃^--N.At 6 h,NH₄⁺-N had been completely degraded,with a removal rate of 100%,and NO₃^--N also decreased simultaneously until 24 h.The removal rate reached 98.6%,and there was almost no accumulation of NO₂^--N.When Na Cl concentration was 0～30 g/L,the NH₄⁺-N removal rate was more than 99%,which could not only remove nitrogen without salt,but also had a certain salt tolerance.The strain grew well in the NH₄⁺-N concentration of 200～500 mg/L.When the initial NH₄⁺-N concentration was 200 mg/L,the NH₄⁺-N removal rate reached 66.4%,and the 24 h average nitrogen removal rate was 5.53 mg/L/h.The strain had a certain phenol tolerance,and the removal rate was greater than 99%when the phenol concentration was 200 mg/L and 400 mg/L.The strain had a great potential in practical wastewater treatment because of its tolerance to complex environment.The successful amplification of hao and nar G key denitrification genes proved the heterotrophic nitrification-aerobic denitrification function of the strain from the gene level.Combined with the heterotrophic nitrification-aerobic denitrification experiment,the denitrification pathway of the strain was preliminarily speculated:The nitrification path was NH₄⁺-NH₂OH-NO₂^--NO₃^-,and the denitrification path was NO₃^--NO₂^--NO-N₂O-N₂.In conclusion,the new heterotrophic nitrification-aerobic denitrification strain JG441 has strong nitrogen removal efficiency and adaptability to complex environment,which makes it have a wide range of application and application potential in practical wastewater treatment.